RPMs drop below idle after throttle
Thread Starter
11 Second Club
iTrader: (14)
Joined: Nov 2004
Posts: 1,653
Likes: 1
From: Michigan (Macomb or Lansing)
RPMs drop below idle after throttle I have a 404 ls2, ported l92s heads, 240s/250s cam 114+3, and fast 102/102.
My rpms drop too fast past idle after throttle and I often have to heel-toe/tap the gas to keep it from stalling. Once idling, it is very stable.
I think I am about to go back to a stock tune and start from scratch.
Say I went to a stock tune, copied over my VE,MAF, and Fueling tables, what else do I need to mess with to fix this problem? I know you usually have to adjust etc scalar number for the 102mm throttle body. I can then do a cold start idle scan for the RAF. Anything else crucial?
My rpms drop too fast past idle after throttle and I often have to heel-toe/tap the gas to keep it from stalling. Once idling, it is very stable.
I think I am about to go back to a stock tune and start from scratch.
Say I went to a stock tune, copied over my VE,MAF, and Fueling tables, what else do I need to mess with to fix this problem? I know you usually have to adjust etc scalar number for the 102mm throttle body. I can then do a cold start idle scan for the RAF. Anything else crucial?
We have real close setups, I have a 402, TEA LS6 stage 2 heads, Fast 102/102, 242/250 113+4.
My car is doing the same thing. I have done a lot to try and get rid of it. The first thing I noticed was the throttle follower keeping the IAC open to long after the throttle is slammed shut. I set my decays to 3 across the board and zeroed out the delay. Now the IAC closes really fast. It also seems that it may be timing related. Make sure you have a smooth transition from your idle to main timing tables. For some reason mine seems to do it less with less timing at idle.
It really is a pain in the ***.
My car seems to loose too many IAC counts at hot idle. I have to crack the throttle blade open to get it to start good cold and to keep it from maxing the IAC out all the way to 310, but this causes me to have really low IAC counts when its hot.
My car is doing the same thing. I have done a lot to try and get rid of it. The first thing I noticed was the throttle follower keeping the IAC open to long after the throttle is slammed shut. I set my decays to 3 across the board and zeroed out the delay. Now the IAC closes really fast. It also seems that it may be timing related. Make sure you have a smooth transition from your idle to main timing tables. For some reason mine seems to do it less with less timing at idle.
It really is a pain in the ***.
My car seems to loose too many IAC counts at hot idle. I have to crack the throttle blade open to get it to start good cold and to keep it from maxing the IAC out all the way to 310, but this causes me to have really low IAC counts when its hot.
The follower helps keep the airflow rate-of-change to
something the idle RPM control loop can follow without
"winding up".
Fat idle mixture is one thing that tends to make motor
step-air idle loop response slow, and unstable. And it's
a common outcome of cam swaps, anything that degrades
low-RPM volumetric efficiency enriches the actual idle
mixture by the back door.
Tuning trouble is, you can't really "get at" the region below
idle RPM, the 400RPM column is the other end of your VE air
mass interpolation and all you can do is eyeball it or guess
at where the curve says it's headed (if the rest of the curve
is realistic).
There are also things you can do to the idle RPM loop P,I,D
params to improve stability given a more-laggy motor, but
the motor ought not to be laggy to begin with. I messed
with mine, some, but control theory is not something I'm
real good at.
something the idle RPM control loop can follow without
"winding up".
Fat idle mixture is one thing that tends to make motor
step-air idle loop response slow, and unstable. And it's
a common outcome of cam swaps, anything that degrades
low-RPM volumetric efficiency enriches the actual idle
mixture by the back door.
Tuning trouble is, you can't really "get at" the region below
idle RPM, the 400RPM column is the other end of your VE air
mass interpolation and all you can do is eyeball it or guess
at where the curve says it's headed (if the rest of the curve
is realistic).
There are also things you can do to the idle RPM loop P,I,D
params to improve stability given a more-laggy motor, but
the motor ought not to be laggy to begin with. I messed
with mine, some, but control theory is not something I'm
real good at.
The follower helps keep the airflow rate-of-change to
something the idle RPM control loop can follow without
"winding up".
Fat idle mixture is one thing that tends to make motor
step-air idle loop response slow, and unstable. And it's
a common outcome of cam swaps, anything that degrades
low-RPM volumetric efficiency enriches the actual idle
mixture by the back door.
Tuning trouble is, you can't really "get at" the region below
idle RPM, the 400RPM column is the other end of your VE air
mass interpolation and all you can do is eyeball it or guess
at where the curve says it's headed (if the rest of the curve
is realistic).
There are also things you can do to the idle RPM loop P,I,D
params to improve stability given a more-laggy motor, but
the motor ought not to be laggy to begin with. I messed
with mine, some, but control theory is not something I'm
real good at.
something the idle RPM control loop can follow without
"winding up".
Fat idle mixture is one thing that tends to make motor
step-air idle loop response slow, and unstable. And it's
a common outcome of cam swaps, anything that degrades
low-RPM volumetric efficiency enriches the actual idle
mixture by the back door.
Tuning trouble is, you can't really "get at" the region below
idle RPM, the 400RPM column is the other end of your VE air
mass interpolation and all you can do is eyeball it or guess
at where the curve says it's headed (if the rest of the curve
is realistic).
There are also things you can do to the idle RPM loop P,I,D
params to improve stability given a more-laggy motor, but
the motor ought not to be laggy to begin with. I messed
with mine, some, but control theory is not something I'm
real good at.
It does seem to get better after a couple revs and the LTFT, STFT start to pull fuel.
